A patent application has been published for alternate alcohol recovery methods by distillation, under WO 00/23402 (Fortum Patent), which is incorporated herein by reference. Prior art relates to the use of tertiary butyl alcohol (TBA) for the purpose to control the reaction selectivity. This is described in Petro-Tex Chemical Company U.S. Pat. No. 4,100,220 of Jul. 11, 1978.
As described in WO 00/23402, the addition of water and C3-C6 alcohol is used to control the conversion and the selectivity of the dimerization reactions. C3 through C6 alcohols are formed in the dimerization process through the reaction of water with C3–C6 olefins present in the hydrocarbon feed. The feedstock primarily comprises C4 olefins and paraffins, but may also contain some propylene, and C5–C6 olefins and paraffins.
In the dimerization, an acidic catalyst is used, preferably, ion-exchange resin catalyst. However, as catalysts can be used zeolites and other inorganic catalysts. The ion exchange resin catalyst can comprise sulphonic acid groups and it can be prepared by polymerizing or copolymerizing aromatic vinyl compounds and, thereafter, sulphonating. As examples of aromatic vinyl compounds the following may be mentioned: styrene, vinyl toluene, vinyl naphthalene, vinyl ethyl benzene, methyl styrene, vinyl chlorobenzene, and vinyl xylene. An acidic ion-exchange resin contains typically in average 1.3 . . . 1.9, even up to 2 sulphonic acid groups per one aromatic group. Preferred resins are those based on copolymers of aromatic monovinyl compounds and aromatic polyvinyl, in particular divinyl, compounds, in which the concentration of polyvinylbenzene is approximately 1 . . . 20 wt-% of the copolymer. The particle size of the ion-exchange resin is preferably approximately 0.15 . . . 1 mm.
In addition to the resins already described, also perfluorosulphonic acid resins consisting of copolymers of sulphonylfluorovinyl ethyl and fluorocarbon compounds can be used. Various suitable ion-exchange resins are commercially available, an example of these is Amberlyst 15.
The feedstock for the dimerization contains isobutylene. Depending of the origin of the feedstock the concentration of isobutylene may vary from 10 wt-% to 100 wt-%. Typical feedstock sources are C4 streams from refinery crackers (e.g. FCC, TCC, DCC, RCC), C4 dehydrogenation units (e.g. Catofin, Oleflex) and also isobutylene manufactured from chemicals where isobutylene content may be more than 90 wt-%.
FIG. 1 describes one typical dimerization process with alcohol recovery. The feed (F) is water washed in extraction column 4 and sent to reaction zone (1). The reaction effluent (R1) is distilled in product distillation column (2) for separation of C4 fraction (D1). The bottom product (B1) is directed for further distillation in column 3. The distillate (D2) contains some C5 to C8 hydrocarbons and alcohols formed in the reaction zone and this distillate is routed back into the reaction zone. The bottom product (P1) from column 3 makes the dimerization product.